The current petrochemical industry is based on the inexpensive and efficient transformation of a few platform chemicals into a wide array of products including solvents, fine chemicals, and monomers for modern plastics. Recently, concerns over sustainability have motivated a return to natural feedstocks; this trend is particularly evident in the polymer industry where consumer awareness of the adverse environmental impacts of nondegradable plastics has driven the commercialization of biodegradable polymers (e.g., the polyesters polylactide and polyhydroxyalkanoates). Despite efforts over the past decade, there exist few methods for efficient, environmentally benign processes for monomer synthesis from biomass.
Organic acids obtained via fermentation of glucose provide an opportunity for synthesis of diols and triols from biomass. Itaconic acid (IA) was termed one of the top-12 building block chemicals in 2004 due to its potential value as a precursor for C5 chemicals (e.g., 2-methyl-1,4-butanediol and (α or β)-methyl-γ-butyrolactone) (T. Werpy, G. Petersen, A. Aden, J. Bozell, J. Holladay, J. White, A. Manheim, D. Eliot, L. Lasure, S. Jones, Top Value Added Chemicals from Biomass. Volume 1-Results of Screening for Potential Candidates from Sugars and Synthesis Gas, DTIC Document, 2004.). Globally, 80,000 tons of IA are produced per year using Aspergillus terreus in a high yielding fermentation process (0.72 g/g from glucose, with titers of up to 86 g/L) (M. G. Steiger, M. L. Blumhoff, D. Mattanovich, M. Sauer, Front. Microbiol. 2013, 4, 1-5; and M. Okabe, D. Lies, S. Kanamasa, E. Y. Park, Appl. Microbiol. Biotechnol. 2009, 597-606). Mesaconic acid (MA), an isomer of IA, has similar potential as a precursor and was recently produced using E. coli (J. Wang, K. Zhang, Metab. Eng. 2015, 30, 190-196). The low cost of itaconic acid (˜$2 kg−1), enables its use in synthetic resins, plastics, rubbers, surfactants and oil additives (M. Besson, P. Gallezot, C. Pinel, Chem. Rev. 2014, 114, 1827-1870; and A. J. J. Straathof, Chem. Rev. 2014, 114, 1871-1908). However, the current production capacity of itaconic acid exceeds its demand.
Mevalonic acid (MLA) is a third organic acid efficiently produced from the fermentation of carbohydrates (˜80 g L−1 titer using E. coli) (M. Xiong, D. K. Schneiderman, F. S. Bates, M. A. Hillmyer, K. Zhang, Proc. Natl. Acad. Sci. 2014, 111, 8357-8362). MLA is a potentially valuable precursor for synthesis of C6 alcohols, ethers and lactones. However, there are few reports outlining efficient, aqueous-based, processes for production of diols from these C5 and C6 acids.
A prominent challenge in replacing petrochemical polymers with bio-derived alternatives is the efficient transformation of biomass into useful monomers. More efficient methods of converting carboxylic acid containing compounds, for example from biomass, to more valuable and useful compounds, for example monomers, are therefore necessary.